UKHO produces Bristol Channel ENC with 1m contours

6 February 2018

The UK Hydrographic Office
(UKHO) has released details of a new Electronic Navigational Chart (ENC) which
could help to improve situational awareness and safety. Developed to cover an
area of the Bristol Channel known as 'The Bridge', this high density ENC
displays depth contours at 1m intervals, allowing ECDIS to set safety contours
at corresponding levels to support navigation through shallow water.

ECDIS will select safety contours based on a safety contour depth value set by
the mariner. As most charts contain depth contours at intervals of 2, 5, 10, 20
and 30 metres, ECDIS will sometimes have to set a safety contour deeper than
the value set by the mariner. As a result of this, ships navigating in
shallower areas like The Bridge have had to cross the safety contour and
override ECDIS alarms, as they have more clearance than indicated. Disabling
these alarms not only increases administrative burden and alarm fatigue, but
also means that alarms will not indicate when the ship is actually approaching
depths of insufficient under keel clearance.

To overcome this challenge, the UKHO has been working with partners to adapt
this ENC to include 1m depth contours. In addition to safety benefits, this
could also bring a significant commercial benefit to cargo owners and ship and
port operators, as ships can be more confident about the true depth of water
under the keel - thereby increasing ships' cargo-carrying capacity.

To create the ENC, the UKHO worked with the manufacturers of their cartography
software to develop a new tool that automatically processes billions of
bathymetric data points to draw 1m contours. These are then confirmed within
the software to ensure compliance with the strict international standards for
all ECDIS systems. Finally, these are manually checked by a cartographer to
confirm accuracy.

This charted area with high density contours was then issued digitally through
the Admiralty Vector Chart Service (AVCS), allowing safety contours at key
areas to be drawn by ECDIS with 1m accuracy. This helps to reduce stress on the
bridge and can give crews a greater degree of confidence on the approach for
the safety of cargo and ship.

Chris Berkley, a Master Mariner and Product Manager at UKHO, commented: "Marking
depth contours at five-metre intervals made complete sense when it was being
drawn by hand on paper or read off a physical chart by a mariner - one-metre
contours can be close together and confusing when applied over wide areas. The
advantage of digital navigation on ECDIS is that we can now switch from
five-metre contouring to higher density one-metre contouring in areas where it
is useful.

"During this project, UKHO's hydrographic database team developed a tool
that fits into our business-as-usual charting methods to create an ENC for a
geographic feature called The Bridgein the Bristol Channel and Severn Estuary.
In this location, silt collects to form an area of water that is far shallower
than the rest of the channel. Ships must pass over 'The Bridge' to get to the
Ports of Bristol or Gloucester. However, even though most ships can safely
transit this area, it is beyond the safety contour for many commercial ships.
Effectively, ships entering the Port of Bristol need to knowingly ignore their
training and cross the safety contour - setting off multiple alarms, causing
lots of disruption, and creating significant paperwork for the master to
explain.

"With the new and now in-use AVCS ENC for this area, we have solved this
problem and masters and pilots can now navigate the area safely and in
accordance with the rules on safety contours."

The UKHO is now extending the format to other ports and channels in the UK and
around the globe which are experiencing similar challenges, thereby supporting
greater navigational safety and efficiency